One hundred mosaic embryos transferred prospectively in a single clinic: exploring when and why they result in healthy pregnancies.

Objective: To investigate the parameters of mosaicism and the biological mechanisms leading to healthy pregnancies from mosaic embryo transfers.

Design: Prospective study.

Setting: IVF center and associated research laboratory.

Assessment of aneuploidy concordance between clinical trophectoderm biopsy and blastocyst.

Study Question: Is a clinical trophectoderm (TE) biopsy a suitable predictor of chromosomal aneuploidy in blastocysts?

Summary Answer: In the analyzed group of blastocysts, a clinical TE biopsy was an excellent representative of blastocyst karyotype in cases of whole chromosome aneuploidy, but in cases of only segmental (sub-chromosomal) aneuploidy, a TE biopsy was a poor representative of blastocyst karyotype.

What Is Known Already: Due to the phenomenon of chromosomal mosaicism, concern has been expressed about the possibility of discarding blastocysts classified as aneuploid by preimplantation genetic testing for aneuploidy (PGT-A) that in fact contain a euploid inner cell mass (ICM). Previously published studies investigating karyotype concordance between TE and ICM have examined small sample sizes and/or have utilized chromosomal analysis technologies superseded by Next Generation Sequencing (NGS).

Accurate quantitation of mitochondrial DNA reveals uniform levels in human blastocysts irrespective of ploidy, age, or implantation potential.

Objective: To accurately determine mitochondrial DNA (mtDNA) levels in human blastocysts.

Design: Retrospective analysis.

Setting: IVF clinic.